Effect of calcium on the potassium flux into the exudate of excised maize roots

Summary The effect of varying calcium concentration in the medium on the potassium flux into the exudate has been studied. In media of low ionic strength (o.1 mM KCl) the potassium flux, J _K, was significantly increased by increasing the calcium concentration of the medium. But in higher ionic strength media (10 mM) KCl) there was no increase in J _K as the calcium concentration of the medium was increased. The effect of external sodium concentration on J _K was also studied. These results are discussed in relation to present theories of salt and water movement into the plant root. It is concluded that two pathways potentially exist for movement of salts to the exudate stream: firstly, via a symplasm and secondly, through the cell wall pathway. But is is further concluded that the cell wall pathway, at normal physiological ionic strengths, is not available for salt transport due to co-ion exclusion by the fixed negative charges.     

Effect of exogenous calcium on post-thaw growth recovery and subsequent plant regeneration of cryopreserved embryogenic calli of <Emphasis Type="Italic">Hevea brasiliensis</Emphasis> (Müll. Arg.)

A reliable cryopreservation technique was developed for friable embryogenic callus lines of Hevea brasiliensis. The study showed that reducing the CaCl₂ concentration of the pre-culture medium from 9 mM to 1 or 0 mM CaCl₂ before cryopreservation promoted post-thaw callus growth, 1 mM being the optimum CaCl₂ concentration for embryo regeneration. Post-thaw callus proliferation decreased in line with the increase of plated callus weight. The effect of cryopreservation was assessed on 39 independent lines showing that cryopreservation did not affect embryogenic and plant regeneration for a majority of lines. The decrease in CaCl₂ concentration of the pre-culture medium led to a drop in callus calcium content indicating a direct link between the CaCl₂ concentration of the pre-culture medium and the endogenous calcium content of the calli. It also highlighted the implication of tissue calcium content in cryotolerance. Callus water status and the different ways by which calcium could prevent cryoinjury is also discussed.     

A mathematical analysis of water and solute transport across the root of Ricinus communis

Summary A mathematical analysis of the relationship between the flux of water, f _H2_O, and the flux of potassium f _K, to the xylem of exuding root systems of Ricinus communis, is presented. Previous analyses (Baker and Weatherley, 1969; Minchin and Baker, 1969) have indicated the presence of a water dependent and a water independent f _K both of which vary with the external concentration of potassium, Cm, supplied as potassium nitrate.The present analysis reveals that whereas at Cm values<1 mM both components of f _K contribute ions to the osmotically active solutions within the osmotic barrier, at Cm values>1 mM only the water dependent f _K is responsible for the osmotic work. This suggests that the ions are released within different regions of the stele. It is proposed that at cm values<1 mM both components are released from the inner stelar tissues whilst at higher Cm values the water dependent f _K is released from the outer stelar tissues. This requires that the solute permeability of the plasmalemma of the outer stelar tissues increases markedly at or about Cm values of 1 mM.It is postulated that the required separation of the two f _K components within the stelar symplasm at Cm values>1 mM is due to the water independent f _K being in a bound state, possibly being transported along a chain of binding sites whilst the water dependent f _K is in a free state within the aqueous phase of the cytoplasm.     

Water dependent and water independent fluxes of potassium in exuding root systems of Ricinus communis

Summary The flux of water, , to the xylem of exuding root systems of Ricinus communis was controlled using a range of mannitol concentrations permitting the influence of this water flux on the potassium flux, f _K, to be studied. The relationship between and f _K thus obtained was investigated, for a number of external concentrations of potassium, Cm, supplied as potassium nitrate. An analysis of these data indicated the presence of a water dependent and a water independent f _K both of which varied with Cm. The water dependent f _K shows a parabolic relationship with Cm for Cm values <1 mM followed by a sharp inflection and decline at higher Cm values whereas the water independent f _K shows an hyperbolic relationship over the same range of Cm values.Uptake of potassium by exuding root systems was measured and shown to be dependent on the solute potential of the medium. The uptake was also shown to exhibit a dual absorption isotherm the kinetics of which indicate a low Km system (system 1) and a high Km system (system 2). The Km value obtained for system 1 is very similar to that obtained for the water independent f _K. It is postulated that the water independent f _K is contributed by that portion of f _K arriving in the stele via the cortical symplast and is directly dependent on Cm. The water dependent f _K is contributed by those ions moved across the root in response to centripetal water movement through the cortical cell walls.     

The Effects of Inorganic Elements on the Reduction of Phytophthora Stem Rot Disease of Soybean, the Growth Rate and Zoospore Release of Phytophthora sojae

The effects of several inorganic elements contained in B5 medium on Phytophthora stem rot disease reduction of Glycine max (L.) Merr. cv. Chusei‐Hikarikuro, fungal growth of Phytophthora sojae isolate and zoospore release were investigated. Application of B5 solution and macro inorganic nutrients in the B5 medium prior to inoculation significantly inhibited infection, compared with controls. Various concentrations of KNO₃, (NH₄)₂SO₄, MgSO₄, CaCl₂ and NaH₂PO₄ in the presence of macro inorganic nutrients were investigated in an effort to determine the elements most effective in suppressing the incidence of disease. A concentration of 2.47–24.7 mm KNO₃ and 0.1–10.2 mm CaCl₂ greatly inhibited infection. Although mycelium growth of the isolate was affected by the potassium and calcium concentration, no significant relationship was observed between inhibition of the growth rate and disease reduction at 2.47 mm KNO₃ and 0.1–5.1 mm CaCl₂ application. Disease suppression recorded in laboratory experiments using pathogen mycelium was due to the response of plant tissues rather than a direct inhibition of pathogen fungal growth by the application of potassium or calcium. The extent of disease reduction was related to an increased potassium and calcium uptake by plants, suggesting that the effective elements in reducing Phytophthora stem rot were potassium and calcium. The presence of 2.47–247 mm KNO₃ and 5.1–10.2 mm CaCl₂ decreased the release of zoospores, although 0.1–2.5 mm CaCl₂ significantly induced zoospore release. These results suggest that applying a solution containing more than 2.47 mm of potassium and 5.1 mm of calcium can decrease the incidence of disease in agricultural fields by the inhibition of zoospore release.     

Effect of NaCl and CaCl<Subscript>2</Subscript> on growth and contents of minerals,chlorophyll, proline and sugars in the apple rootstock M 4 cultured <Emphasis Type="Italic">in vitro</Emphasis>

The apple (Malus domestica Borkh) rootstock M 4 shoots were grown in vitro for 4 weeks on Murashige and Skoog (MS) medium containing three NaCl concentrations (35, 100 and 200 mM) in combination with two CaCl₂ concentrations (5 and 10 mM). Inclusion of 10 mM CaCl₂ in the medium, in the presence of 35 mM NaCl, significantly increased the number of shoots and the fresh mass compared to 5 mM CaCl₂. The number of shoots, length of shoots, and the fresh mass of cultures were very low in the presence of 100 and 200 mM NaCl, independently of CaCl₂ concentration of the medium. By increasing NaCl and CaCl₂ concentrations in the culture medium, contents of N, Na, Cl, proline and soluble sugars in plantlets increased, whereas K, Mg, B, Zn and chlorophyll content decreased in comparison to the control.     

Effets de l’Oxygenation du Milieu d’Incubation des Cotyledons de Ricin sur les Flux de Protons et sur l’Absorption du Saccharose

Some of the effects of oxygen concentration in the external medium bathing castor bean cotyledons were investigated. At 700 μM O₂, the sucrose-dependent proton influx was dependent on external pH while sucrose influx was independent of pH between 4,5 and 6; proton influx and sucrose influx were both dependent on external sucrose concentration; both were saturated above 50 mM sucrose. The stoichiometry H+/S decreased with increasing pH and sucrose concentration. These data were consistent with the results obtained in stirred or aerated external medium. Oxygen consumption, acidification of the medium, sucrose-dependent proton influx and sucrose uptake increased with increasing oxygen concentration up to 700 μM where saturation was reached. Bubbling with air (O₂, 160 μM) resulted in the same increase despite lower oxygen concentration. It is suggested that not only O₂ concentration but also CO₂ concentration act on O₂ consumption, and proton and sucrose fluxes.

---

     

Inactivation of ntcA gene revealed differential proteome expression and induction of some hypothetical proteins in the cyanobacterium Anabaena sp. PCC 7120 and its derivative ntcA mutant under different levels of calcium

Abstract

Calcium is an important macronutrient for both prokaryotes and eukaryotes. It acts as an important second messenger mediating rapid response to environmental conditions. The present investigation deals with proteome profiling of Anabaena 7120 and its derivative ntcA mutant in response to varied calcium doses (0, 1 and 10?mM CaCl₂). Concentration of 1?mM CaCl₂ salt was the optimum concentration whereas 10?mM CaCl₂ was the inhibitory concentration for both the wild type and mutant strains. The results showed highly significant alteration in terms of protein abundance and differential response related to key processes of photosynthesis, energy and metabolism, nitrogen metabolism, oxidative and antioxidative defence, transport and signalling and fatty acid metabolism. In the wild type proteins related to photosynthesis and nitrogen metabolism showed upregulation at 1?mM CaCl₂ concentration while antioxidative defence related proteins were down-regulated. In the mutant however, proteins related to photosynthesis and nitrogen metabolism exhibited severe down-regulation. Some hypothetical proteins were also realized during proteome analysis. Overall, our results suggested that NtcA have a potential role in regulation of calcium ion dependent key processes underlying in various metabolic activities of the cyanobacterium Anabaena 7120.     

A comparison of potassium translocation in excised roots and intact maize seedlings

Summary The water and potassium fluxes exuded by excised primary roots of maize seedlings are compared with the rate of wet weight increase and of potassium uptake by the growing tissue of the shoots of intact seedlings. The exuded potassium flux from 1 mM KCl solution as the bathing medium is found to correspond very closely to the potassium uptake by the shoots of seedlings of idenfical age and history as the excised roots.     

Glucose and octanoate utilization by isolated adult rat heart cells

Rat heart muscle cells continue to beat in the isolated state apparently independent of any innervation. The oxidation of ¹⁴C-glucose to ¹⁴CO₂ was linear for at least 60 minutes of incubation. The rate of glucose oxidation rose rapidly up to a medium glucose concentration of 2.5 mM and then plateaued. Lactate production reached a maximum at 5 mM glucose. Glucose uptake was linearly related to the concentration up to 40 mM. The addition of octanoate reduced, but did not eliminate, glucose oxidation. Octanoate utilization increased with increasing concentration and reached a maximum at 2 mM. The oxidation of octanoate was linearly related to the time of incubation for at least 90 minutes. The presence of glucose, at a concentration of 1.25 mM or higher, increase the oxidation of octanoate by the heart cells. The metabolic parameters measured with the isolated heart cells gave values comparable to those obtained with the perfused rat heart. Decreasing or increasing the concentration of sodium, potassium or magnesium did not effect the oxidation of either glucose or octanoate with the exception that when sodium was increased above 200 mM, a significant increase in glucose oxidation was observed. In contrast, the addition of calcium to a calcium free medium increased glucose oxidation, reaching a maximum at 0.2 mM calcium. The oxidation of octanoate reached a maximum at 0.2 mM and then decreased significantly with increasing calcium concentration. The metabolic activity appears to be independent of the concentration of sodium, potassium or magnesium. In contrast, the isolated heart cell is very sensitive to a change in calcium concentration.     

ON THE ROLE OF CALCIUM IONS IN OOCYTE MATURATION IN THE POLYCHAETE CHAETOPTERUS PERGAMENTACEUS*

The germinal vesicle of mechanically released Chaetopterus oocytes disintegrates in natural sea water (NSW), but not in artificial sea water of normal composition (ASW), calcium-free sea water (CaFSW), magnesium-free sea water (MgFSW) or calcium and magnesium-free sea water (CaMgFSW). Several methods of inducing oocyte maturation using chemically well-defined medium have been established. (1) Germinal vesicle breakdown was induced by the treatment of immature oocytes with KCl (60 mM) in ASW or MgFSW. The presence of Ca²⁺ is necessary for inducing oocyte maturation with high potassium concentration. “Differentiation without cleavage” was observed after this treatment. (2) Trypsin (0.3%) induced oocyte maturation in ASW, but not in CaFSW. Oocytes matured in this manner developed to trochophores upon insemination. (3) Immature oocytes, treated with isotonic CaCl₂ for less than 1 min and then transferred to ASW, underwent germinal vesicle breakdown. The oocytes were arrested at the first meiotic metaphase and upon insemination developed to trochophore larvae. (4) Tetracaine (0.4 mM) induced oocyte maturation in the absence of Ca²⁺ in the medium. In ASW, CaFSW or CaMgFSW containing the drug, oocytes were arrested at the first meiotic metaphase, while in MgFSW with tetracaine they developed parthenogenetically up to the 4- and 8-cell stages. The role of calcium in oocyte maturation was established and its importance was discussed based on the results obtained with the different ways of inducing oocyte maturation.     

Apoplastic transport across young maize roots: effect of the exodermis

The uptake of water and of the fluorescent apoplastic dye PTS (trisodium 3-hydroxy-5,8,10-pyrenetrisulfonate) by root systems of young maize (Zea mays L.) seedlings (age: 11–21 d) has been studied with plants which either developed an exodermis (Casparian band in the hypodermis) or were lacking it. Steady-state techniques were used to measure water uptake across excised roots. Either hydrostatic or osmotic pressure gradients were applied to induce water flows. Roots without an exodermis were obtained from plants grown in hydroponic culture. Roots which developed an exodermis were obtained using an aeroponic (=mist) cultivation method. When the osmotic concentration of the medium was varied, the hydraulic conductivity of the root (Lp _r in m³ · m⁻² · MPa⁻¹ · s⁻¹) depended on the osmotic pressure gradient applied between root xylem and medium. Increasing the gradient (i.e. decreasing the osmotic concentration of the medium; range: zero to 40 mM of mannitol), increased the osmotic Lp _r. In the presence of hydrostatic pressure gradients applied by a pressure chamber, root Lp _r was constant over the entire range of pressures (0–0.4 MPa). The presence of an exodermis reduced root Lp _r in hydrostatic experiments by a factor of 3.6. When the osmotic pressure of the medium was low (i.e. in the presence of a strong osmotic gradient between xylem sap and medium), the presence of an exodermis caused the same reduction of root Lp _r in osmotic experiments as in hydrostatic ones. However, when the osmotic concentration of the medium was increased (i.e. the presence of low gradients of osmotic pressure), no marked effect of growth conditions on osmotic root Lp _r was found. Under these conditions, the absolute value of osmotic root Lp _r was lower by factors of 22 (hydroponic culture) and 9.7 (aeroponic culture) than in the corresponding experiments at low osmotic concentration. Apoplastic flow of PTS was low. In hydrostatic experiments, xylem exudate contained only 0.3% of the PTS concentration of the bathing medium. In the presence of osmotic pressure gradients, the apoplastic flow of PTS was further reduced by one order of magnitude. In both types of experiments, the development of an exodermis did not affect PTS flow. In osmotic experiments, the effect of the absolute value of the driving force cannot be explained in terms of a simple dilution effect (Fiscus model). The results indicate that the radial apoplastic flows of water and PTS across the root were affected differently by apoplastic barriers (Casparian bands) in the exodermis. It is concluded that, unlike water, the apoplastic flow of PTS is rate-limited at the endodermis rather than at the exodermis. The use of PTS as a tracer for apoplastic water should be abandoned. Received: 9 October 1997 / Accepted: 5 February 1998     

Effects of bicarbonate on fluid and electrolyte transport by the guinea pig gallbladder: A bicarbonate-chloride exchange

Summary Fluid transport and net fluxes of Na, K, Cl and HCO₃ by guinea pig gallbladder were investigatedin vitro. A perfused gallbladder preparation was devised to simultaneously study unidirectional fluxes of²²Na and³⁶Cl. The net Cl flux exceeded the net Na flux during fluid absorption in the presence of HCO₃. This Cl excess was counter-balanced by a net HCO₃ secretion: a HCO₃–Cl exchange. PGE₁ reversed the direction of fluid transport and abolished the net Cl flux. The magnitude of the HCO₃ secretion remained unchanged, but shifted from a HCO₃–Cl exchange to a net secretion of NaHCO₃ and KHCO₃. Furosemide inhibited both the HCO₃–Cl exchange and HCO₃ secretion after PGE₁ without influencing fluid absorption. Ouabain inhibited the HCO₃–Cl exchange as well as fluid absorption; only the effect on the HCO₃ secretion was entirely reversible. Secreted HCO₃ appeared not to be derived from metabolic sources since HCO₃ secretion was abolished in a HCO₃-free bathing medium. HCO₃ secretion was also dependent on the Na concentration of the bathing fluid. Three lines of evidence are presented in favor of an active HCO₃ secretion in guinea pig gallbladder. HCO₃ is secreted against: (i) a chemical gradient, (ii) an electrical gradient and (iii) the direction of fluid movement under control conditions.     

Relative roles of Ca2+, Sr2+, Ba2+ and Mg2+ in controlling lens permeability characteristics

The effects of barium, strontium and magnesium upon lens permeability characteristics were studied in the presence and absence of 2 mM calcium in the bathing medium. Permeability characteristics were determined by measuring lens potential, resistance and ⁴²K efflux rates. Barium and strontium at equimolar concentrations to calcium were able to substitute for calcium in controlling lens sodium permeability. Magnesium was ineffective in this respect.Small changes in resistance and ⁴²K efflux rates occurred when calcium was eliminated from bathing solution containing either 2 mM barium or strontium. These changes were interpreted to be the result of an increase in lens permeability to potassium. When 2 mM strontium was added to calcium-containing solution, there was no significant change in the electrical or flux parameters of the lens. However, the addition of 2 mM barium to calcium-containing solution resulted in a 54% increase in lens resistance and a 13 mV depolarization. These observations indicated a barium-induced decrease in lens permeability to potassium, and this was confirmed by an observed decrease in ⁴²K efflux rate constant under similar experimental conditions.The rapid time course of all the observed changes implies that they are the result of changes in the permeability characteristics of membranes lying close to the surface of the lens.     

Effect of sodium,potassium, and calcium ions on electroreceptor function in catfish

Impulses from single electroreceptors (small pit organs) of catfish (Ictalurus nebulosus) were recorded during stimulation by square pulses. Solutions with different concentrations of potassium, sodium, and calcium ions were applied to the pore of the receptor. Solutions with a low CaCl₂ concentration did not alter the responses of the receptor. Calcium ions in concentrations of over 5 mM increased the threshold of the response to electrical stimulation. The threshold to anodal stimulation was increased in solutions of 2 mM sodium and potassium and no response was given to a cathodal stimulus. The effect of 2 mM solutions of NaCl and KCl was abolished by the addition of 0.4 mM CaCl₂ or by application of a long anodal stimulus of high intensity (10⁻⁸∓10⁻⁷ A/mm²). Increasing the potassium ion concentration to 10–20 mM restored normal receptor function but a further increase led to elevation of the threshold. The action of an electric current is compared with the action of the ions.     

Role of 1,25-Dihydroxyvitamin D3 and Extracellular Calcium in the Regulation of Proliferation in Cultured SH-SY5Y Human Neuroblastoma Cells

This study examines the effects of 1,25-dihydroxyvitamin D₃ [1,25(OH)₂D₃] on SH-SY5Y human neuroblastoma cells cultured in the presence of medium containing varying concentrations of calcium (0.1, 0.9, 1.4, 1.8 mM). Pyruvate kinase activity was assayed in SH-SY5Y cells incubated in variable calcium medium with or without 1, 10 or 100 nM 1,25(OH)₂D₃ for 48 h. The enzyme levels showed a significant increase in comparison with control, when the cells were incubated with 100 nM hormone in the presence of 0.1 mM calcium, while pyruvate kinase activity decreased, when the cells were treated with 100 nM 1,25(OH)₂D₃ in the presence of 1.8 mM calcium. The proliferative activity of SH-SY5Y was dependent on the extracellular concentration of calcium, being the highest at 1.8 mM calcium and completely absent at 0.1 mM calcium. In the presence of 1,25(OH)₂D₃, at the three concentrations used and after 48 h incubation, a significant decrease in cell number was always observed, without a direct correlation between 1,25(OH)₂D₃ effect and calcium concentration in the medium. [³H]Thymidine incorporation in SH-SY5Y cells significantly increased in comparison with control, when the 48 h incubation with 1, 10 or 100 nM 1,25(OH)₂D₃ was carried out in the presence of 0.1 mM calcium, while, at the other calcium concentrations, the hormone did not cause any significant change in this parameter. The treatment of SH-SY5Y cells with 1 nM 1,25(OH)₂D₃ for 48 h did not affect cell morphology, when 0.1 mM calcium was present, while, in the medium containing 1.8 mM calcium, the treated cells showed a slight trend to differentiation. The differentiating effect of 10 M all-trans retinoic acid, even if incomplete after 48 h treatment, was only observed in the cultures grown in 1.8 mM calcium, in comparison with those maintained in 0.1 mM calcium.     

Calcium Binding Ability of Recombinant Buffalo Regucalcin: A Study Using Circular Dichroism Spectroscopy

Regucalcin is a calcium regulating multifunctional protein reported to have many important functions like calcium homeostasis, anti-oxidative, anti-apoptotic and anti-cancerous functions. Although it is demonstrated as a calcium regulating protein, the calcium binding ability of regucalcin is still a controversy. The main reason for the controversy is that it lacks a typical EF hand motif which is common to most of the calcium binding proteins. Even though many studies reported regucalcin as a calcium binding protein, there are some studies reporting regucalcin as non-calcium binding also. In the present study, we investigated the calcium binding ability of recombinant buffalo regucalcin by assessing the secondary structural changes of the protein using circular dichroism spectroscopy after adding Ca²⁺ to the protein solution. Two types of calcium binding studies were done, one with different concentration of calcium chloride (0.5 mM CaCl₂, 1 mM CaCl₂, 2 mM CaCl₂) and other at different time interval (no incubation and 10 min incubation) after addition of calcium chloride. Significant structural changes were observed in both studies which prove the calcium binding ability of recombinant regucalcin. A constant increase in the α-helix (1.1% with 0.5 mM CaCl₂, 1.4% with 1 mM CaCl₂, 3.5% with 2 mM CaCl₂) and a decrease in β-sheets (78.5% with 0.5 mM CaCl₂, 77.4% with 1 mM CaCl₂, 75.7% with 2 mM CaCl₂) were observed with the increase in calcium chloride concentration. There was a rapid increase in α-helix and decrease in β-sheets immediately after addition of calcium chloride, which subsides after 10 min incubation.     

An Analysis of the Leakages of Sodium Ions into and Potassium Ions out of Striated Muscle Cells

Net sodium influx under K-free conditions was independent of the intracellular sodium ion concentration, [Na]_i, and was increased by ouabain. Unidirectional sodium influx was the sum of a component independent of [Na]_i and a component that increased linearly with increasing [Na]_i. Net influx of sodium ions in K-free solutions varied with the external sodium ion concentration, [Na]_o, and a steady-state balance of the sodium ion fluxes occurred at [Na]_o = 40 mM. When solutions were K-free and contained 10^-4 M ouabain, net sodium influx varied linearly with [Na]_o and a steady state for the intracellular sodium was observed at [Na]_o = 13 mM. The steady state observed in the presence of ouabain was the result of a pump-leak balance as the external sodium ion concentration with which the muscle sodium would be in equilibrium, under these conditions, was 0.11 mM. The rate constant for total potassium loss to K-free Ringer solution was independent of [Na]_i but dependent on [Na]_o. Replacing external NaCl with MgCl₂ brought about reductions in net potassium efflux. Ouabain was without effect on net potassium efflux in K-free Ringer solution with [Na]_o = 120 mM, but increased potassium efflux in a medium with NaCl replaced by MgCl₂. When muscles were enriched with sodium ions, potassium efflux into K-free, Mg⁺⁺-substituted Ringer solution fell to around 0.1 pmol/cm²·s and was increased 14-fold by addition of ouabain.     

The Effect of Hydrostatic Pressure Gradients on the Movement of Potassium across the Root Cortex

Transpiration reduces the hydrostatic pressure in the xylemand water moves into the root and across the root cortex inresponse to the pressure gradient so produced. This effect wassimulated by raising the pressure on the external medium surroundinga detopped root system. The flux of sap from the stem stumpand the concentration of potassium in the sap were measuredand the flux of potassium into xylem obtained as (sap flux Xconcentration of potassium). The application of a pressure of 2 atm. caused an approximatelyfourfold increase in potassium flux. This increase was independentof the presence of potassium in the external medium and wasdue, therefore, to an efflux of ions already stored in the roottissues. The effect was specifically due to hydrostatic pressureand not to the D.P.D. difference across the cortex, and wascaused, in part at least, by an increase in the permeabilityof the tissues to iona. This is evident since the increasedpotassium flux occurred in response to pressure, even when theconcentration of potassium in the xylem increased at the sametime, thus precluding any ‘dilution effects‘. It was confirmed that metabolic inhibitors and low temperaturereduce the sap flux but leave the concentration of the sap unchanged.Under a pressure gradient, however, there was an even greaterporportionate reduction of sap flux by equivalent concentrationsof inhibitor or low temperature and the concentration of potassiumin the sap gradually increased. Adding calcium or magnesium ions to the medium caused an increaseof potassium concentration in the sap, demonstrating exchangeprocesses in the transpiration pathway. The difficulty of framing a hypothesis to cover all the factsis discussed and it is tentatively suggested that movement acrossthe cortex to the xylem is a catenary process in which soluteand water move independently at one stage and together as asolution at another stage.     

Microencapsulation of yeast cells in the calcium alginate membrane

Summary Cells of Saccharomyces cerevisiae (ATCC 24858) were encapsulated in the calcium alginate membrane and cultured. Swelling of the capsule was prevented by adding 0.2 g CaCl₂ to 1 L growth medium. The dry cell concentration based on the inner volume of the capsule reached 309 g/L, which was much higher than could be obtained by cell entrapment. All the cells remained inside the capsule during the cultivation. The flux of CO₂ through the capsule membrane increased approximately twice by adding a nonionic surfactant to the CaCl₂ solution during the step of capsule formation.